This invention relates to a heat insulating coating material for use in protecting machinery from high temperatures in a reducing or oxidizing atmosphere, in lining the interior of a heating furnace, and in preventing a substance such as steel from being partially heated or retarding the cooling rate of a substance in the heat treatment.
Hitherto, a heat insulating material, which can be used in a reducing or oxidizing atmosphere, has been applied by mechanically fixing asbestos fibers, glass fibers or fabrics thereof or adhering them together with a binder, or applying the mixture of asbestos or light-weight refractory particles with clay, refractory cement or inorganic binders to substrates.
Such prior applying processes do not only require skill and a long period of time when the heat insulating material is to be applied to substrates of, for example, steel, but also they have such drawbacks that said material is peeled from said substrates when heated, cooled or subjected to mechanical impact, because of weak adhesiveness of said material to metallic surfaces of said substrates.
The causes of the peeling are believed that the adhesion between heat insulating materials and metallic surfaces is not strong, the strength of heat insulating materials is low due to weak bonding force of said materials per se, oxides on metallic surfaces are reduced when an atmosphere is reducing, or oxides are formed on metallic surfaces when an atmosphere is oxidizing.
It is considered that a binder having a low melting point is used and vitrified to prevent the peeling, but in such case the molten binder is penetrated into aggregates or reacted with aggregates, so that the heat insulating material is totally made vitreous, and thus a porosity is lowered and the insulating effect is lowered. Where an atmosphere is oxidizing, resultant oxides are diffused into a binder, the bond strength of the binder is lowered and resultant coatings are weak.